Method of reinforcing green sand cores



March 31, 1964 J DEWEY T 3,126,595

METHOD OF REINFORCING GREEN SAND CORES I AND MOLDS WITH FOAM POLYMERCOATED METAL ELEMENTS Filed Feb. 20, 1961 INVENTORS. John L. Dewey Roy6. 6/0700 fiukwvflfMo fl TTORNEYS United States Patent METHUD 0FREINFORCING GREEN SAND CORES AND MOLDS WITH FUAM POLYMER COATED METALELEMENTS John L. Dewey, Pleasant Hill, and Roy C. Simon, Walnut Creek,Calif., assignors to The Dow Chemical Company, Midland, Mich, acorporation of Delaware Filed Feb. 20, 1961, Ser. No. 90,532 6 Claims.(Cl. 2214) This invention relates to the manufacture of cast metalarticles and more particularly relates to improvements in the making ofreinforced sand molds and cores for the casting of metals. It pertainsespecially to improvements in embedding reinforcing metal rods, bars,strips, bonds, webs and the like in sand molds and cores prior to curingthe same.

It is common practice to embed reinforcing metal rods, bars, webs andthe like in green sand molds and cores to strengthen the same to inhibitor prevent breaking or cracking of the same during handling in the greenstate prior to curing or hardening of the shaped molds or cores. Ingeneral, reinforcing of green sand cores is necessary when cores ofrelatively large size are prepared in order to facilitate handling andto avoid cracking or breaking of the green sand cores prior to theirbeing cured or hardened to a condition suitable for use in the castingof metals.

However, because of differences in the coefficients of expansion of thecured sand cores and metals, e.g. iron or steel, the embeddedreinforcing metal rods, bars, or webs expand more rapidly or to agreater degree than the sand core, by heating upon pouring of the moltenmetal to be cast, with the result that the mold or core is cracked orbroken and imperfect castings are obtained.

It has now been discovered that these difliculties can be prevented orsubstantially inhibited by embedding in the green sand core, reinforcingmetal rods, bars, strips, bands or webs having on the surfaces thereofan adherent layer or coating of a foamed organic polymer of a thicknesssufiicient to provide a cushion for expansion of the reinforcing metalwithout producing appreciable stress or strain in the cured sand mold orcore, upon being heated by the pouring of the molten metal to be castinto the mold.

It has further been found that the foam coated reinforcing metal rods,bars, strips, bands, webs, or the like are equally as effective forstrengthening the green sand molds or cores to facilitate handling andprevent cracking or breaking in the green state as are uncoated metalreinforcing rods, bars, webs and the like, and are particularlyeffective for preventing breaking or cracking of the cured sand moldsand cores in use for the casting of metals.

The coating can be a foam of any organic polymer such as a foamedpolyurethane, foamed phenol-formaldehyde resins, foamed epoxy resins,foamed vinyl resins, foamed olefin polymer, or foamed alkenyl aromaticpolymers, e.g. styrene polymers. Foamed alkenyl aromatic polymers, arepreferred. By an alkenyl aromatic polymer is meant the normally solidhomopolymers and copolymers containing in chemically combined, i.e.polymerized and interpolymerized, form at least 50 percent by weight ofat least one alkenyl aromatic compound having the general formula edhydrocarbon radicals of the benzene series and R is a member of thegroup consisting of hydrogen and the 3,126,595 Patented Mar. 31., 1964See methyl radical. Examples of suitable alkenyl aromatic polymers arethe homopolymers and copolymers of one or more alkenyl aromaticcompounds such as styrene, vinyltoluene, vinylxylene, ethylvinylbenzene,isopropyl styrene, tert.-butylstyrene, ar-dichlorostyrene,methoxystyrene, fluorostyrene and the like, copolymers of one or more ofsuch alkenyl aromatic compounds and a minor proportion of anothercopolymerizable ethylenically unsaturated monomer such as methylmethacrylate or acrylonitrile; and graft copolymers e.g. copolymers offrom 1 to 15 percent by weight of natural or a synthetic rubber and amonoalkenyl aromatic compound such as styrene, vinyltoluene, vinylxyleneand the like, and mechanical blends of alkenyl aromatic resins and from1 to 15 percent by weight of natural or a synthetic rubber.

Methods for making foamable granules from such polymers are well known.For example, foamable granules can readily be prepared by polymerizingthe monomer, e.g. styrene, in admixture with a volatile organic fluidsuch as pentane, hexane, petroleum ether, dichlorodifluoromethane,dichlorotetrafluoroethane, and the like, under pressure until a solidpolymer is obtained, cooling the product under pressure, releasing thepressure and thereafter crushin grinding or cutting the solid materialto a granular form. In an alternative procedure, the monomer can bepolymerized in admixture with the volatile foaming agent while dispersedas droplets in an inert liquid medium such as water or brine, underpressure, whereby the foamable granules are obtained. In anotherprocedure, the foamable granules can be prepared by suspending granulesof the polymer in an inert liquid medium such as water or brine andheating the granules of the polymer in admixture with the volatileorganic foaming agent at temperatures between about 30 and 125 C. underpressure, whereby the resin granules are impregnated with the foamingagent, then cooling the mixture, releasing the pressure, separating anddrying the impregnated polymer. The polymer can contain from about 0.03to about 0.4 gram molecular proportion of the volatile organic foamingagent per grams of the polymer, or stated differently foamable polymercompositions containing from about 3 to 8 percent by weight of pentaneor an equivalent foaming proportion of a volatile organic fiuid compoundare satisfactory.

The foam coated metal rods, bars, strips, bands or webs to be employedas reinforcement in the green sand cores or molds can be prepared in anyusual way. For example, metal bars, rods or webs, e.g. a screen orcheckerboard panel, can be sprayed with a liquid mixture of a foamablepolyurethane resin which is allowed to foam up on the metal to form alayer or coating of the foam of a desired thickness. In the case ofusing foamable beads or granules of the polymer such as foamable alkenylaromatic polymer beads, the metal bar, rod, or web is first coated witha suitable adhesive such as a liquid curable phenol-formaldehyde resinor an epoxy resin to form a tacky coating on the metal, then contactingthe adhesive coated metal with a body of the foamable beads or granulessuitably of sizes of from about 0.5 to 5, preferably from about 1 to 3,millimeters in diameter to adhere the beads to the metal in asubstantially uniform layer, and thereafter heating the adhered layer ofbeads in any usual way such as by steam, hot air, in an oven, infra-redlamps, or in a porous mold, to foam the beads and cure the adhesive,whereby the metal rod, bar or web is uniformly or is substantiallyuniformly coated with a layer of the foamed polymer. Such layer of thefoamed polymer can be of a thickness of from about 1 to 20, preferablyfrom about 2 to 20, millimeters or more thick. For best results thecoating of the foamed polymer should be of substantially uniformthickness and should cover all or substantially all parts of the metal,particularly the ends of the rods or bars so as to provide a cushion ofthe foamed polymer for lengthwise, or other, expansion of the rods orbars without transfer of such stress directly against the surroundingsand core or mold.

The foamed polymer coated reinforcing rods or bars and the manner inwhich they are embedded in a green sand core or mold in practice of theinvention is described more particularly with reference to theaccompanying drawing wherein:

MG. 1 is a diagrammatic sketch partly in section showing an enlargedview of steel reinforcing rod coated with a layer of a foamed styrenepolymer adhesively bonded to the rod by a heat-curablephenol-formaldehyde resin.

FIG. 2 is a diagrammatic sketch showing in cross section an arrangementof foamed polymer coated steel reinforcing rods embedded in the sandcore for the casting of a metal valve body, egg. from molten stainlesssteel or ordinary carbon steel.

In the drawing the numeral 3 indicates a metal valve body in crosssection showing a sand core indicated generally by the numeral 4 havinga plurality of foamed polymer coated steel reinforcing rods 5 embeddedin the sand core 4, and

FIG. 3 is a diagrammatic sketch showing in cross section a sand mold 6for the casting of a truck metal rear axle and differential housing 7employing a sand core 8 having embedded therein foam polymer coatedmetal reinforcing rods 9.

In practice, among expansion areas where defects usually occur becauseof stress or strain resulting from unequal expansion of the reinforcingmetal rods and the sand core when the reinforcing metal is not coatedwith a foamed polymer are those points or areas where bends occur in thereinforcing metal and where linear expansion of the reinforcing rodscauses excessive stress or strain, e.g. at the ends of the casting shownin FIG. 3. However, when foam polymer coated metal rods are employed asreinforcing material in accordance with the invention in making thegreen sand core which is subsequently cured or hardened then used in thecasting of metal, the effect of any stress or strain resulting fromunequal expansion of the metal reinforcing rods, which are required tostrengthen the green sand core but are not necessary in the cured core,is avoided because the foam provides a cushion for absorbing thedifference in expansion of the materials upon heating and prevents suchstress or strain from being transferred to the sand core.

The number, size and shape of the reinforcing metal bars, rods or websto be embedded in the green sand core or mold is dependent upon thesize, shape and configuration of the core or mold and will be apparentto those skilled in the art, it being necessary only in practice of theinvention that the reinforcing metal elements be coated with a layer oforganic polymer foam of a thickness sufiicient to prevent orsubstantially inhibit the effect of unequal expansion of the cured sandcore or mold and the metal reinforcing elements embedded therein and tocushion such expansion so as not to produce a resultant stress or strainbetween sand core or mold and the reinforcing metal.

The following examples illustrate ways in which the principle of theinvention has been applied, but are not to be construed as limiting itsscope.

Example 1 Carbon steel rods 0.5 inch in diameter and about 7 feet longcommonly employed as reinforcing elements in the making of sand coresfor a cast stainless steel valve body similar to that shown in FIG. 2 ofthe drawing were coated by brushing with a liquid curablephenol-formaldehyde resin and while sticky were rolled in a bed offoamable polystyrene granules of sizes between about 0.8 and 1.5millimeters in diameter and containing about 6.5 percent by weight ofpentane as the foaming agent, thereby forming a layer of the polystyrenebeads adhered to the rods. The head coated rods were heated with steamand were foamed to form a substantially continuous layer of the foamvarying from about 9.5 to 12.5 millimeters thick surrounding the steelrod. The foam coated rods were embedded as reinforcing elements in agreen sand core for a cast stainless steel valve body weighing about2000 pounds and similar to that shown in FIG. 2 of the drawing. The foamcoating on the reinforcing rods was tough, durable and was not broken bypacking of the green sand in the core box. The green sand corecontaining the foam polymer coated steel reinforcing eiements was curedand was subsequently employed as the core for casting a stainless steelvalve body similar to that shown in FIG. 2 of the drawing and having theapproximate internal dimensions of 30 inches, 20 inches and 9 inchesrespectively, for the valve body outlets, and a wall thickness whichranged from 6 inches to 5 inches to 3.5 inches, respectively, for saidoutlets. The foam polymer coated steel reinforcing elements weresatisfactory for strengthening the green sand core, and the cured sandcore was substantially better than a sand core made with uncoated steelreinforcing elements, for the casting of the stainless steel metal valvebody.

Example 2 Carbon steel rods 0.25 inch in diameter and of lengths from 6to 8 to 24 inches long were dipped into a liquid phenolic resin, wereremoved and allowed to drain for a period of from 30 to 60 seconds, thenwere dipped or plunged into a body of foamable polystyrene beads ofsizes between about 0.8 and 1.5 millimeters diameter, containing about6.5 percent by weight of petroleum ether (B.P. 30-45 C.) as blowingagent, thereby adhering a layer of the foamable beads to the resincoated steel rods. The head coated rods were heated in an oven at atemperature of C. for a period of from 2 to 5 minutes, thereby causingthe beads to foam. The rods were removed from the oven, and while stillin a foamed and plastic condition, the layer of foam was pressed withgloved hands and shaped to a substantially uniform layer covering theentire length and ends of the rods to a depth of the foamed layer offrom about 6.5 to 9.5 millimeters.

The foam coated rods were employed as reinforcing elements in the makingof a sand core for the casting of a metal rear axle and differentialhousing for a motor vehicle by embedding the foam coated rods in thegreen sand core in an arrangement similar to that shown in FIG. 3 of thedrawing. The green sand core was cured and was employed for the castingof a steel rear axle and differential housing for a commercial motorvehicle similar to that shown in FIG. 3. The resulting casting was aperfect replica of the mold cavity.

In contrast, when a similar sand core was prepared employing the 0.25diameter steel rods, without the polystyrene foam coating, asreinforcing elements and the cured core was used to cast a steel rearaxle and differential housing it was found that linear expansion of thereinforcing rods caused breaking of the sand core at each of its ends.The resulting casting was unusable.

We claim:

1. In a method for making sand cores for the casting and molding ofmolten metals wherein the green sand core contains reinforcing metalelements embedded therein to strengthen the core prior to curing thesame, the improvement which comprises coating the reinforcing metal withan adherent layer of from about 1 to 20 millimeters thick of a foamedorganic polymer and embedding the foam coated reinforcing metal in thegreen sand core and thereafter curing said core.

2. A method according to claim 1, wherein the organic polymer is afoamed thermoplastic alkenyl aromatic polymer.

3. A method according to claim 2, wherein the foamed alkenyl aromaticpolymer is polystyrene.

4. A method for making sand cores for the casting and molding of moltenmetals Which method comprises forming and shaping a green sand coreWhile embedding Within said core reinforcing metal elements coated withan adherent layer of from about 1 to 20 millimeters thick of a foamedorganic polymer and thereafter curing said green sand core.

5. A method for making sand cores for the casting and melding of moltenmetals, which method comprises forming and shaping a green sand corewhile embedding Within said core reinforcing metal rods coated With anadherent layer of from about 1 to 20 millimeters thick of a foamedthermoplastic alkenyl aromatic polymer, and thereafter curing said greensand core.

6 6. A method according to claim 5, wherein said foamed alkenyl aromaticpolymer is polystyrene.

References Cited in the file of this patent UNITED STATES PATENTS2,045,556 Almen June 23, 1936 2,903,018 Goff Sept. 8, 1959 2,958,905Newberg et al Nov. 8, 1960 2,960,482 Henning Nov. 15, 1960 3,066,365Moore Dec. 4-, 1962 FOREIGN PATENTS 386,302 Great Britain Apr. 9, 1931

1. IN A METHOD FOR MAKING SAND CORES FOR THE CASTING AND MOLDING OFMOLTEN METALS WHEREIN THE GREEN SAND CORE CONTAINS REINFORCING METALELEMENTS EMBEDDED THEREIN TO STRENGTHEN THE CORE PRIOR TO CURING THESAME, THE IMPROVEMENT WHICH COMPRISES COATING THE REINFORCING